1. Field of the Invention
The presently disclosed subject matter relates to an apparatus and a method for estimating mammary gland content rate, particularly, to technology for estimating a mammary gland content rate for each pixel in a breast image from only the breast image obtained by radiographing a breast by a mammography imaging apparatus.
2. Description of the Related Art
A breast is mainly constituted of mammary gland tissue and adipose tissue, and the ratio of the mammary glands in the breast is called a mammary gland content rate. The mammary gland content rate is extremely useful in accurately knowing the character of a breast, and is medically indispensable information. For example, a study suggests that a correlation exists between the mammary gland content rate and the risk of cancer.
At present, classification and evaluation of the composition of a breast (the degree of mammary gland involution is classified into four stages of adipose, scattered mammary gland, nonuniform high density, and high density) are performed qualitatively based on the contrast difference of mammary gland and adipose by vision, but the evaluations are likely to be inconsistent depending on radiogram interpreters, and more quantitative evaluation is required.
Conventionally, as the method for quantitatively evaluating a mammary gland content rate, there is the method disclosed in Japanese Patent Application Laid-Open No. 2002-125961. In this method, mammary glands are classified, for example, with the density of the pectoral muscle as the reference, the variation of the mammary gland region is converted into histogram, and what is the mammary gland ratio in the breast is determined (paragraph [0029] of Japanese Patent Application Laid-Open No. 2002-125961).
Meanwhile, there is proposed the method for estimating a mammary gland content rate for each of pixels in a breast image. By calculating the mammary gland content rate for each of the pixels, application to various applications is enabled (aid of diagnosis, CAD (Computer-Aided Detection), image processing condition setting, and QA). In “Measurement of Glandular Dose Using Digital Mammogram”, Medical Imaging and Information Sciences, Vol. 24, No. 1, pp. 6-12, 2007, the mammary gland content rate is calculated for each of pixels based on the dose ratio (transit dose/exposure dose), breast mass thickness, and the relationship between a pixel value and a mammary gland content rate (previously obtained relational expression).
Further, “Volumetric Breast Density Estimation From Full-Field Digital Mammograms”, IEEE Trans. MEDICAL IMAGING, Vol. 25, No. 3, 2006 discloses the technology for calculating the attenuation coefficients of mammary gland and adipose based on the information of the X-ray tube voltage obtained from the imaging apparatus, the target/filter and the breast mass thickness, and estimating the volume of the mammary glands based on the isopachic correction image estimated by “Thickness correction of mammographic images by anisotropic filtering and interpolation of dense tissue”, Proc. SPIE (Medical Imaging: Image Processing), Vol. 5747, pp. 1521-1527, 2005, and the respective attenuation coefficients.